This invention relates generally to formation machines and processes and, more particularly, to a process and machine for forming bistable snap-disks.
Bistable snap-disks are typically utilized as mechanical cycling components in fluid operated switching devices, pressure cycling devices, and other mechanisms utilizing a two-position, bistable, snap-action switch. See, for example, U.S. Pat. No. 5,198,631. Such snap-disks include a convex configuration and a concave configuration to engage or disengage electrical contacts and open and close an electrical circuit, respectively. The snap-disks snap, or xe2x80x9ctripxe2x80x9d between a convex and concave configuration depending on the application of sufficient external forces on one of the sides of the disk, such as, for example, a pressure, and snap or xe2x80x9cresetxe2x80x9d into an original configuration when those external forces fall below a predetermined value. The required forces causing a snap-disk to trip or reset between the convex and concave configurations, and vice-versa, vary from application to application, but for a given disk, the trip and reset force values are usually unequal.
Bimetallic and monometallic snap-disks are typically formed with a full radius punch that forms a curved shape in the central portion of the disk. Precise formation tolerances are required in forming snap-disks so that the disks adequately react to external forces, such as temperature or pressure differentials, in a given switch application. The precise formation tolerances, however, are difficult to consistently achieve using current snap-disk formation methods. Consequently, a one hundred percent sort of formed snap-disks is often required, and yields of acceptable snap-disks upon initial formation are as low as thirty percent. The low yield of acceptable disks decreases manufacturing efficiency and raises the costs of production of the snap-disks.
Accordingly, it would be desirable to increase the yield of acceptable snap-disks upon initial formation and decrease production costs in snap-disc formation.
In an exemplary embodiment of the invention, a snap-disk form assembly and method includes a form station coupled to a feedback station so that the formation of the snap-disks may be monitored in real time as the snap-disks are formed. Thus, correction of any deficiency in the formation process is detected and redressed nearly instantaneously.
More particularly, the form station includes a plurality of cams, with each cam including a respective tool. The plurality of cams and tools in the form station stretch the sides of disk blanks to plastic deformation and thereby form the reset and trip sides of the disk.
The feedback station includes a cam-driven probe that sequentially monitors the required peak force to snap the form disks into a respective alternative configuration after they are formed, and monitors the required peak reset force to snap the form disks into their original configuration. A force transducer is connected to the probe, and the probe is brought into engagement with one of the sides of the snap-disks. Therefore, the probe applies a force to the snap-disk that is measured by the force transducer and used for feedback control of the form station. Force is applied by the probe until the disk trips, and the measured peak force that caused the disk to trip is recorded by a feedback station controller. The force applied by the probe is then decreased until the disk resets into its original configuration, and the peak force before the disk resets is also recorded by feedback station controller.
A mean peak trip force value and a mean rest trip force value are calculated for a predetermined number of disks, and the mean values are compared to a predetermined trip target value and a reset target value, respectively. The operation of the tools in the form station are then adjusted in real time, based upon the comparison of the measured mean value to the target value, to change the required peak snap force of successively formed disks and bring successive disks within desired peak snap force tolerances.
Using statistical process control feedback from the feedback station to adjust formation parameters in the form station increases the initial pass rate of the snap-disks and lowers the costs of snap-disk production.